Loudspeaker system



Feb. 7, p B, RE D LOUDSPEAKER SYSTEM 6 Sheets-Sheet l Filed April 11 Feb. 7, 1967 P. B. REED 3,302,748

LOUDSPEAKER SYSTEM Filed April 11, 1963 6 Sheets-Sheet 2 M D Y ES E R mm m m.

Feb. 7, 1967 6 Sheets-Sheet 5 Filed April 11 1963 FEGB Feb, 7, 1967 REED 3,32,748

LOUDSPEAKER SYSTEM Filed April 11, 1963 6 Sheets-Sheet 4 FIG.9

Feb. 7, 1967 p, B REED 3592,74

I LOUDSPEAKER SYSTEM Filed April 11. 1963 6 Sheets-Sheet 5 260 25e 23% m A252 Feb. 7, 196? Filed April 11, 1963 P. B. REED LOUDSPEAKER SYSTEM 6 Sheets-Sheet 6 United States Patent 3,302,748 LOUDSPEAKER SYSTEM Prentiss B. Reed, 4104 Huntington Road, Huntsville, Ala. 35802 Filed Apr. 11, 1963, Ser. No. 272,390 Claims. (Cl. 181-31) This invention relates to loudspeaker systems employing a dense gas as the acoustic coupling medium, for general use such as with radio and television receivers, phonographs and public address and auditorium sound systems. It relates more particularly to methods and means for maintaining nearly uniform, the acoustic response characteristics of such loudspeaker systems as they undergo ambient change in temperature and barometric pressure to which normally exposed.

As used herein, the term dense gas denotes any gas or mixture of gases, of whatever composition, having a density greater than that of air. Where the trade names such as Freon-1 14, Freon-12 are used, the corresponding trade equivalents of F-114, F-12 and others are included within the intent. The term acoustically conducting means, as used herein, denotes any acoustically conducting apparatus capable of confining the dense gas coupling medium as well as of conducting sound between a sound generator diaphragm and the air. The term accommodator is defined as a means or apparatus used to react to the ambient changes in temperature and barometric pressure to which loudspeaker systems are exposed withdrawing or receiving excess volumes of confined dense gas (or of space-compensating air, as the case may be) and providing additional volumes of the gas (or air) as required. To accommodate is the verb form of so doing, and to compensate is used synonymously therewith. The terms loudspeaker system and loudspeaker combination are used herein synonymously to include, among other things, any dense gas used as the internal acoustic coupling medium within and about the other elements of the system. While not so specified in every instance, where the containment of any gas or air is specified or implied, the containing device is intended as substantially impervious to the passage of gases except through any openings or passages specified. The term ambient effects is used to mean the normally expected changes in temperature and in barometric pressure experienced in an ordinary environment. Compliance is understood generally to be the reciprocal of,stifiness, and in a membrane is inversely related to tension or tightness.

Earlier sound reproducing equipment has employed a confined dense gas as the acoustic coupling medium, but has used substantially tight enclosures, filled with a dense gas confined therein by a membrane. Some such equipment has used internal pressures above atmospheric. Some arrangements have resulted in uncontrolled variations of internal pressure and variations in the tightness of confining membranes caused by ambient elfects. The result has been changing response characteristics, especially at the lower frequencies, unacceptable resonances in tight membranes, a spurious crinkling sound from loose membranes, and, under extreme conditions, the threatened or actual rupture of membranes. No such equipment has, as yet, appeared on the commercial market, despite the small size and high quality of sound possible with dense gas coupled loudspeaker systems.

Among the objects of this invention are: maintaining nearly uniform the acoustic characteristics of the dense gas used as the coupling medium; maintaining a substantially uniform compliance in any membrane used to confine the dense gas and transmit sound; holding within acceptable limits, variations in the response characteristics of the loudspeaker system with ambient change; and avoiding the etfects of high velocity transverse waves in mem- 3,302,748 Patented Feb. 7, 1967 branes. A further object of the invention is to prevent the overstretc'hing or bursting of membranes. An additional object is to permit tuning the response characteristics of a particular loudspeaker system to suit taste or necessity. A further broad object is to make practical for ordinary use, loudspeaker systems employing a dense gas as the acoustic coupling medium, thereby permitting general enjoyment of the remarkable and outstanding quality of reproduction possible with such loudspeakers.

These and other objects are achieved, in general, by the use of an accommodator apparatus, communicating with confined portions of a dense gas used as the acoustic coupling medium and subject to ambient effects, the accommodator reacting to these effects also, receiving or withdrawing excess volumes of confined gas and providing additional quantities, as required.

Other objects and advantages of this invention will further become apparent hereinafter, and in the drawing, in which:

FIGURE 1 is an elevation of one form of dense gas coupled loudspeaker system:

FIGURE 2 is a sectional plan on lines 2-2 and 2A2A of the system shown in FIGURE 1;

FIGURE 3 is a sectional elevation of another form of dense gas coupled loudspeaker system:

FIGURES 4 through 7 show a further form of dense gas coupled loudspeaker system, in which:

FIGURE 4 shows the system in elevation:

FIGURE 5 is a sectional elevation of the system as shown in FIGURE 4:

FIGURE 6 is a section through the axis of the diffusion type pressure reducer shown in FIGURE 5:

FIGURE 7 is an expanded portion of FIGURE 6:

FIGURE 8 shows a further form of dense gas coupled loudspeaker system:

FIGURE 9 shows a further form of dense gas coupled loudspeaker system:

FIGURE 10 shows a further form of dense gas couple-d loudspeaker system:

FIGURE 11 shows a further form of dense gas coupled loudspeaker system.

In describing the preferred embodiments of the invention illustrated in the drawing, specific terminology will be resorted to for the sake of clarity. However, it is not intended to be limited to the specific terms so selected, and it is to be understood that each specific term includes all technical equivalents which operate in a similar manner to accomplish a similar purpose.

Referring to FIGURES l and 2: 1 is a sound generator, comprising the diaphragm or cone of a cone type speaker mounted in an acoustic coupling device consisting of a corner enclosure 2 of impervious construction, but communicating through tubing 16 and 17 with a bellows and having a rear aperture 3 and containing a dense gas indicated by the symbol at 4. The interior 7 of the enclosure confines a portion of dense gas at the rear of the sound generator diaphragm, and the acoustically conducting means comprising the membrane 5 and walls of the chamber 8 confines a portion of the dense gas in front of the diaphragm. The rear aperture 3 is enclosed by the impermeable laminated membrane 9 in its mounting 10 with the end closures 11 and 12, additional portions of the dense gas moving freely through the aperture 3, between the space within the membrane 9 and the enclosure interior. A capped tube 13, leading to the chamber 8 is used for filling with the dense gas, and has a capillary 14 opening into the chamber 7 to join the two gas portions and so equalize pressure. The capped tube 15 is used as a vent in filling the chamber 8. The tubing 16 communicates with the chamber 7, permitting compensation fiow from the tubing 17, and filling through the capped connection 20, the vent for such filling being through the capped tubing 21. An over and under pressure relief valve, 18, communicates with the atmosphere through the filter 19. An accommodator or compensation apparatus in the form of a bellows 22, of any suitable material, attached to a mounting strip 23 in a bellows enclosure 24 and having a vent at25, communicates with the loudspeaker enclosure through the tubing 16 and 17, and by its action accommodates increases and decreases of volume of the dense gas caused by ambient effects. The bellows enclosure has at least one opening to the atmosphere, as shown at 24a. The membranes shown in FIGURES 1 and 2 in their respective mountings, are sealed therein under tension, and the edges of sealants and immediately adjoining zones of the membranes are reinforced on both sides with a suitable flexible element, such as a coating of plastic rubber, to prevent fracture by excessive bending of the film where it joins the sealant. This reinforcement also absorbs transverse waves in the membrane, analogous to the action of elastomers used in controlling edgeflapping in loudspeaker cones. The comm-only used grille cloth and its mounting are wholly conventional, and although intended in such a loudspeaker system, have been omitted from the views to simplify the drawing and its ready understanding. Similarly, it is commonly appreciated that a single bellows may have the capacity to afford accommodation to more than one speaker unit, and that connections therefor may be provided in the gas system for so doing, nevertheless although intended in such a loudspeaker system, such connections have likewise been omitted from the views for simplification.

Referring to FIGURE 3: 26 is a sound generator or reproducer unit of impervious construction, its diaphragm indicated schematically at 27, with a portion of the dense gas 28 confined by the rear chamber of the reproducer unit behind the diaphragm. Another portion of dense gas is confined by the acoustically conducting means comprising the acoustic coupling device, or horn, 30 and membrane 32 in its mounting, in front of the diaphragm, and moves freely in and out of the horn via its mouth. An annular mounting 31, also impervious, substantially surrounds the aperture of the horn, carrying the impermeable membrane, 32, and in turn is mounted on the flexible annular diaphragm 33. The diaphragm is mounted on the horn and permits free motion of the membrane in its mounting, as well as acting as a closure for the contained dense gas. A rod 34 extends across the aperture of the horn, mounted in openings in the horn and turning in frictional bushings, one such bushing being indicated at 35. The ends of the rod are formed as 90 cranks, one such crank being indicated at 36, engaging openings in brackets mounted firmly on the inside of the annular mounting 31, one such bracket being indicated at 37. A similar rod 38 also lies across the aperture of the horn, substantiallyperpendicular to rod 34, mounted in a similar fashion. The combined effect of the cooperating parts including the rods and frictional mountings is such as to constrain the annular mounting 31 to move parallel to the axis of the horn and to remain perpendicular thereto, and to overcome such frictional resistance in such motion as to eliminate any resonance in the motion. By this motion, the annular mounting and membrane act as a bellows, thus accommodating ambient effects. The capped connection and tubing 4-2 communicates variously with the interior of the horn, the interior of the reproducer unit through the capillary 47, thus joining the gas portions and equalizing pressures, and with a valve 43 used in filling the system with gas, and with an over and under pressure relief valve 45 which communicates in turn through a filter 46 with the atmosphere. Capped tubing 44 is used as a vent during filling.

Referring to FIGURES 4 and 5 48 is a sound generator comprising the diaphragm or cone of a cone type speaker mounted in an acoustic coupling device, or enclosure 49,

of impervious construction, with tubing 78 for the flow in and out of gas, in which the rear panel 50, with the inner panel structure 53 and other walls form the rear chamber 55, confining a dense gas portion at the rear of the sound generator diaphragm, and in which the inner panel structure 53 and the aperture panelsSl and 52 form an additional chamber 56 communicating with chamber 55 via a small communicating means, sufficiently small so as to have negligible acoustical influence, consisting of tubing 78 and 79, and via the port 54, through all of which the dense gas moves freely, joining the front and rear gas portions. The walls of the chambers 56 and 6-3, together with the membrane 57 in its mounting 58, comprise portions of an acoustically conducting means that confines a dense gas portion in front of the sound generator diaphragm. A separate and distinct second impermeable membrane 59 in its mounting 60 forms an additional chamber 64 with the membrane 57 and mountings. This chamber does not communicate with the other chambers. A grille cloth 61 in its mounting 62 covers the front of the loudspeaker unit. Shown beneath the enclosure 49 is an accomod ator or bellows apparatus 65, of impervious construction, comprising a front panel 66, rear panel 67, side panels 68 and 69, and bottom: panel 70. A piston, 71, is constrained to move vertically but remaining parallel to the bottom panel by means of the parallel motion hinges 72 and 73. The piston is closed by the piston seal 74, which is sealed likewise to the inside walls of the bellows enclosure. The air vent 75 admits air flow to and from the chamber 76 above the piston. Although not shown in the views for simplicity of presentation, wholly conventional means, such as a predetermined weight of piston 71, or an adjustable weight, spring or torque motor device is intended, to' drive the piston 71 and afford a predetermined or adjustable pressure bias for the enclosed gas. The cappedtubing 77 permits filling through the bellows chamber, tubing 78 communicating between the bellows and the lower portions of chambers 55 and 56-. During filling, venting is accomplished through the capped tubing 79. Filling the chamber 64 between the two membranes is accomplished through capped tubing 80, with venting through capped tubing 81. A container and liquid for gas replenishment, 82, communicates with a dilfusion type cell 83, which in turn communicates via the capped tubing 80 with the chamber 64. A very slow regulated flow of gas, of the order of 1 pound in several years, passes through the space between the two membranes, sweeping out any accumulated components of air or moisture which may have diffused inward-1y through the membrane 59, and passes out by way of the capped tubing 81, the relief valve 84, and the filter 86 to the atmosphere. The dense gas 87 and the dense gas 88 may be of different composition, permitting the use of a gas having optimum acoustic characteristics Within the chambers 55', 56 and 63, and a gas most suitable for dispensing through a diffusion cell within the chamber 64. A relief valve communicates with the chamber 55 and communicates also through the filter 86 with the atmosphere.

Referring to FIGURES 6 and 7: 83 is a diffusion cell, in which 89 is a perforated tube, closed at one end and communicating via the perforations with the interior of a closed diffusion member, 95, sealed to, as well as rolled on it. The outer cylinder 90 with end caps 91 and 92 form an enclosure for the diffusion element as assembled on the perforated tube with the spacers 94 and 94-a. The dense gas at high pressure from the liquid container enters via the tube 93 and surrounds the diffusion memher. The diffusion member, which may be made from flattened polyethylene tubing closed at each end, contains an interior spacer of porous material 9-8, and the successive turns of the diffusion member as assembled on the perforated tube are separated by a similar porous spacer 99.

Referring to FIGURE 8: A sound generator comprising the diaphragm or cone of a cone type speaker is shown mounted on the front panel 102 of an acoustic coupling device, or enclosure 101, having small communicating means, the ducted port 103, tubing 114 and tubing 115, through which the dense gas may move freely, thus joining the front and rear portions of gas. The enclosure walls and panel 102 form a chamber 104 confining a dense gas portion at the rear of the sound generator diaphragm. An acoustically conducting means, comprising membrane 105 in its mounting 106, and the walls of the enclosure and the panel 102, confines a dense gas portion at the front of the sound generator diaphragm. A separate and distinct membrane 108 in its mounting 109, together with the membrane 105 in its mounting 106 form the additional chamber 110. A grille cloth 111 in its mounting 112 covers the front of the enclosure. The chambers 104 and 107 are filled with dense gas 113 through the capped tubing 114 and vented through the capped tubing 115. A desiccator cell which may also contain materials for absorbing carbon dioxide is shown at 116. The chamber 110 is filled with the dense gas 113, but this may be of different composition than that in chambers 104 and 107 if desirable. The capped tubing 117 is used to fill chamber 110, the capped tubing 118 being used as a vent. An accommodator embodying a suitably powered cooling element is shown at 119. 120 is an insulated container with the separator 121 and the outer walls of the container forming the chamber 122.

' The separator 123, outer walls of the container and separator 121 form a chamber 124. The separator 123 and outer walls of the container also form the chamber 125 which has an open end. A cooling element 126 and a heat sink 127, such as a sealed container of water, are shown in chamber 122, as is also the thermal element 128 of the thermostatic valve 129, which operates as a check valve, sealing the contents of container 134 against loss in case of interruptions of long duration to the supply of chill to the cooling element 126. A valve of insulating material 130 mounted firmly on rods 131 and 132, opens or closes the communication of air between chambers 122 and 124. A thermal armature 133 provides a small predetermined bias of cooling to maintain the container 134 and its contents at a temperature close to the boiling point of the liquid when the accommodator is not absorbing or generating gas. The container and contents of dense gas in liquid phase, 134, are normally at substantially atmospheric pressure and at the boiling temperature of the liquid, such as Freonll4, a common refrigerant, which upon vaporization comprises the dense gas 113. The valve 135 of insulating material is mounted so as to move freely on rods 136 and 137, and together with the piston 142 engages spring 135-a, being further constrained to remain perpendicular to the rods by its motion along pin 13-8 fastened to the piston 142. The bellows 139, together with the valves 130, 135 and the rod and sleeve mechanism shown, comprise a volume-sensitive control that communicates with the confined portions of gas and regulates a variable thermal coupling of the container 134 with the cooling element and with the atmosphere. 140 is one of several openings in the outer flange of the bellows allowing free passage of air. 141 is a diaphragm carrying the piston 142. A valve disc 143 is fastened to the piston 142 and carries the rods 136 and 137 firmly attached. While the valve disc and the piston are shown as being firmly joined together, a threaded collar mounted in an annular groove in the piston and engaging threads in the valve disc may be included as a conventional adjustment to vary the separation and thus afford a bias of the null position of the piston, allowing adjustment of pressure within the confined gas. However, being commonly understood, such adjustment means has been omitted from the figure for simplicity. A sleeve 144 is firmly attached to the rod 136 and moves freely through an opening in the separator 123 along rod 131. A flange 145 is firmly attached to the rod 131 and engages spring 146. Similarly, a sleeve 147 is firmly attached to rod 137 and moves freely through an opening in the separator 123 and along rod 132. A flange 148 is firmly attached to rod 132 and engages spring 149. The capped tubing 114 communicates also with the thermostatic valve 129, the bellows 139, and with the over and under pressure relief valve 150, the latter communicating further with the atmosphere through filter 151. The tubing 152 communicates with the thermostatic valve 129 and the container of liquid 134. Double insulated tubing indicated at 153 communicates with the cooling element 126 and a heat exchanger 156 in the cold compartment of a refrigerator or the like, 154, circulating a cooling fluid between the two by thermal convection.

Referring to FIGURE 9: 157 and 159 are loudspeaker units of impervious construction, having small communicating means consisting of capillary 173 and tubing 171, 184 and 187 through which the dense gas 163 moves in and out freely, suitable for one channel of stereophonic reproduction, 158 and 160 being similar units suitable for a second stereophonic channel. 161 is a sound genera tor or reproducer unit of impervious construction, its sound generator diaphragm indicated schematically at 162. The rear chamber of the reproducer unit confines a dense gas portion at the rear of the sound generator diaphragm. The capped tubing 164 is used as a vent during filling. 165 is an acoustic coupling device consisting of a horn of impervious construction, which, together with the membrane 166 in its mounting 167 comprise portions of an acoustically conducting means that confines a dense gas portion in front of the sound generator diaphragm 162. The front of speaker unit 157 is covered by a grille cloth 168 in its mounting 168-41. The capped tubing 169 is used as a vent during filling. Tubing 170 communicates between the rear chamber of the reproducer unit 161 and a mul-ti-position valve 172. Tubing 171 communicates between the lower portion of the horn interior, the multi-position valve 172 and a capillary 173 which communicates further with the chamber behind the diaphragm. The front and rear portions of gas are thus joined. 174 is a sound genera-tor comprising the diaphragm or cone of a cone type speaker, mounted on the front panel 176 of an acoustic coupling device, or enclosure, 175. The walls of the enclosure and the front panel form the chamber 177 and confine a dense gas portion at the rear of the diaphragm of sound generator 174. An acoustically conducting means, comprising membrane 178 in its mounting 179 and the front panel and walls of the enclosure, confines a dense gas portion in front of the sound generator diaphragm. A grille cloth 180 in its mounting 181 covers the front of the enclosure. Valve 183 communicates with the chamber 182 via tubing 184, and with tubing 187, and is used in filling the enclosure with gas. Tubing 185 communicates between the upper part of chamber 182 and the lower part of chamber 177, thus joining the front and rear portions of the gas with a small communicating means. The capped tubing 186 is used as .a vent in filling the enclosure with a dense gas. The tu'bing 187 communicates with the valves 172 and 183, with similar valves at loudspeaker units 158 and 160, and with a measuring unit, 188, in which 189 is an impervious container filled with the dense gas 163. Gas is introduced into the systern by opening any suitable tubing or fitting. A spher ical Helmholtz resonator, 190, with open aperture 191 is mounted within the container 189, and a sound generator 192 is assembled to the resonator and has sealed external connections 193 used during measurements. The tubing 194 communicates between the container 189 and various parts of the accommodator 195. The accom modator employs a suitably powered thermoelectric cooling element, 203, an insulated container for dense gas in liquid phase, 199, and a volume-sensitive control means employing a bellows communicating with the confined portions of gas that actuates conventional signal generating means regulating the direction and intensity of current to the thermoelectric element, described in more detail as follows: 197 is an insulated compartment with insulated walls 198. Within this compartment is a container 199 of dense gas, such as dichlorotetrafiuor-oethane, in liquid phase, the container communicating by tube 200 with a thermostatic valve 201 also within the compartment. A metal cylinder 202 in which the container 199 fits closely, is attached to :a thermoelectric cooling element 203, and acts as a thermal armature. The plate 204 is normally the cold side, and plate 205 normally the hot side, the two plates being substantially insulated by thermal insulation 207. Electrical connections 206 provide power for operation of the thermoelectric element. The plate 205 is attached to a metal sidewall 208 which has external fins 209 for heat rejection. An over and under pressure relief valve 210 communicates via the filter 211 with the atmosphere, and with tubing 194, the latter also communicating with the container 189, the thermostatic valve 201, and a volume-sensitive bellows 225. An external source of A.C. power, 212, is connected to the primary, 214, of the transformer 213, and to the primary, 219, on the movable core 218, of the E-transformer 217. The centertapped secondary 221 on the fixed core 220 of the E-transformer is connected through the diodes 232 and 234 and the variable resistor 233 to a pair of silicon controlled rectifiers 231 and 235, arranged in circuitry as shown, with a secondary 215 of the transformer 213 to furnish controlled direct current of one polarity to the power connection 237 containing a choke coil 236 and leading to the thermoelectric element 203. A similar arrangement connected to secondary 222 furnishes cont-rolled direct current of opposite polarity to the power connection 237. The direction and intensity of current, and hence heating or cooling action, depends on the direction and magnitude of displacement of the movable core, 218, of the E-transformer. The movable core 218 is attached by adjustable link 223 to the piston 224 of the bellows 225.

Referring to FIGURE 10: The enclosure portion, 238, and horn portion, 240, together form an acoustic coupling device of a loudspeaker unit that has tubing 249 and 266 for the free flow in and out of gas, suitable for one channel of stereophonic reproduction, in which 239 is a sound generator comprising the diaphragm or cone of a cone type speaker. 240 is a short horn, reentrant from the panel 241, to which the speaker is firmly mounted at the throat with its rear supported from the back wall of the enclosure. An acoustically conducting means comprising membrane 242 in its mounting 243 and the enclosure walls and panel, and the horn, confines a dense gas portion in front of the sound generator diaphragm. A grille cloth 244 in its mounting 245 covers the front of the enclosure. The chamber 248 at the rear of the enclosure and behind the horn confines a dense gas portion at the rear of the diaphragm. A small communicating means, consisting of tubing 249, communicates between the upper part of the chamber 247 and the lower part of chamber 248,.thus joining the gas portions. The capped tubing 250 provides venting during filling. A heater element 251 warms the contained gas when energized, causing it to expand. The capped tubing 266 communicates with the lower part of chamber 247. 252 is the enclosure portion of a second loudspeaker unit suitable for an additional channel of stereophonic reproduction, similar in all other respects to that just described previously, and communicating with tubing 266 and heater circuit 269. The capped tubing 266 communicates also with an over and under pressure relief valve 267 which communicates further with the atmosphere through the filter 268. The heater circuit 269 leads from the control switch 286 to heater elements 251 and 265. An accommodator comprising a compressor driven by an electric motor, with the heater elements 251 and 265 for auxiliary accommodation, a container, and volumesensitive control means communicating via container 271 and tubing 266 with the confined gas portions, is shown at 270 (except for the heater elements 251 and 265) and is more fully described as follows: 271 is an impermeable container in which other components are placed and are surrounded by the dense gas 246. A capped tube 272 is used in filling the container 271 and other portions of the system with dense gas. A container of dense gas in liquid phase under pressure is shown at 273. The liquid is at ambient temperature and thus under pressure within its container, and is the reservoir for additional gas as required, and to which excess gas is returned under pressure, as necessary. The tube 274 communicates with the space in the container above the liquid level, and with a relief valve 275 which communicates in turn with the atmosphere via tubing 276. Any air contaminants tend to remain gaseous, collecting above the surface of the liquid with cycling, and with accumulation, are expelled through relief valve 275. A second tube 277 enters the container 273 and its open end extends below the level of the liquid more or less to the bottom of the container 'and communicates also with the reversible constant displacement pump shown schematically at 278. The pump communicates with the dense gas within contain-er 271 through filter 279. The pump is connected by shaft 280 to the reversible motor shown schematically at 281, in which 282 is the field coil, 283 the reversing coils, 284 a condenser, parts of a conventional reversing circuit. External A.C. power, 285, is shown connected to the schematic control switch, 286. This switch is actuated by a control link 287, shown schematically, attached to and actuated by the schematic crank 288 which is linked in turn to the motion of the piston 289 of a bellows, 290. The piston area and its total travel may be made sufficiently large to afford a null distance of piston motion between reversals of the control switch in which the bellows acts also to afford a sufiicient accommodation capacity so as to usefully reduce the cycling of the heater elements or pump. Also, the angular relationships among the :poles and contacts of the switch 286 about the axis may be made adjustable. However, such enlargement of bellows element and adjustments for switching angles, although intended in such a loudspeaker system, have been omitted from the views as .being readily understood common practice. The interior of bellows 290 communicates via tubing 291 and the filter 292 with the atmosphere. A sound generator is shown at 293, a predetermined distance from a sound receiver 294, the acoustic path between them being indicated at 295. External connections at 296 are provided for timing measurements in determining gas purity.

Referring to FIGURE 11: 296 is a sound generator comprising the diaphragm or cone of a cone type speaker which is mounted at the throat of one horn portion, 297, which, with a second horn portion, 303, form an acoustic coupling device, or duct. The mouth of horn 297 has sealed thereto a mounting 298 carrying a short cylindrically shaped ring of elastomer, 299, of generally L-shaped cross-section, to which a membrane 300 is sealed, forming, with the horn 297, a chamber 301 and together confining a dense gas portion at the rear of the sound generator diaphragm. The horn 297 is so constructed at its throat as to mount the speaker 296 and also afford a seating at which to join firmly an additional horn 303. This latter horn is so shaped at its mouth as to seat in the opening 313 of 312, a wall, ceilinl panel or enclosure with which associated, and as to provide a seating at which the mounting 304 is sealed, the mounting having a short cylindrically shaped ring of elastomer 305, of generally L-shaped cross-section sealed to it, to which a membrane 306 is sealed, comprising with h-orn 303 and elastomer, portions of an acoustically conducting means that confines a dense gas portion in front of the sound generator diaphragm. A grille cloth 308 in its mounting 309, suitably mounted within the shaping of the mouth of the horn covers the aperture. Capped tubments of the invention.

ing 310, its cap recessed in slot 314 of 312, the wall, ceiling, panel or enclosure with which associated, communicates with the lower portions of chambers 301 and 307, and is used for filling the system with gas. Similar capped tubing, 311, communicates with the upper portions of chambers 301 and 307 and is used for venting during filling, and communicates also with the over and under pressure relief valve 316, which communicates in turn with the atmosphere through filter 317. The tubing communicating between the chambers 301 and 307 comprise small communicating means that join the gas portions. The membranes 300 and 306, moving in and out, stretching their elastomers as required, comprise as well, an accommodator, communicating with the confined gas portions via the mouths of the horns, through which the gas moves freely.

The figures and descriptions used to portray the present invention and its embodiments include the use, as associated system elements, of direct radiating speakers of the cone type with several types of enclosures suitably modified, and combinations of loudspeaker reproducer or drive units and horns, together with portions of a dense gas coupling medium confined in front of and behind the cones or diaphra-gms, and an accommodator communicating with the confined portions of gas in preferred embodi- However, the invention is not limited to combinations which include the use of any particular system elements for attaining the objects of the invention, being limited only by the claims.

Furthermore, the figures and descriptions do not illustrate or describe loudspeaker systems that contain elements of receiver or amplifier devices, as radio and television receiver amplifier and display combination, any or all parts of which may desirably be located within the enclosed volume of dense gas of the present invention, nevertheless, such contained elements enclosed within a dense gas used in this invention are likewise anticipated and included in this invention.

Operation This dense gas coupled loudspeaker system employs a dense gas coupling medium contained within and about acoustic elements, and an accommodator to compensate for expansion and contraction of the confined gas caused by ambient changes in temperature and barometric pressure. Containment is accomplished through use of impervious materials of construction and sealants, and use of a more or less impermeable film, or membrane, at acoustic apertures. The system employs, as the acoustic coupling medium, any of the many suitable dense gases such as Freon-114 (F-114), CClF CClF or dichlorotetrafiuoroethane; Freon-12 (F-12), CCl F or dichlorofiuoromethane; sulphur hexafluoride, SP all being inert and non-toxic, the Freons and their trade equivalents being commonly used as refrigerants and as propellants in household and cosmetic spray can dispensers, SF being used as an inert dielectric. Other dense gases having suitable characteristics, principally those of inertness, suitable boiling point, lack of objectionable odor or toxic properties, and possessed of desirable acoustic properties may be used. The desirable acoustic properties are found in gases having high density and low sound velocity, as compared with air.

An appreciation of the eifect of using Freon-114 rather than air as a coupling medium can be gained from examining the terms and factors of some of the mathematics involved. The classical mathematics expressing the air load on a piston closely approximates the load on a cone, and the greater this loading, the greater the power and efiiciency of the system generally. An approximation for this loading, under certain conditions, is given by Z in the following:

Examining the mechanical resistance term, we find as direct factors, both p, (density) and c, (sound velocity) which may be considered together as the product p c. From Table I, we find that this product for air is about {84, and for Freon-114, about 181, or 2.l6 greater than for air. The mechanical reactance term contains as a direct factor, p, (density), which for Freon-114 is seen to be 6.l5 greater than for air. Thus there is an extensive increase in the loading.

The compliance of an enclosure is given by C in the following:

The expression varies directly as 1/ p6 which for air is 10.5 X10 and for Freon-114 is 1397x10 the latter value being 1.33 greater than that for air. Thus the compliance of an enclosure using Freon-114 is about a third greater than the compliance of the same enclosure using air. This increased compliance is an important factor in achieving the high resolution of acoustical detail in the waveform generated by a dense gas coupling medium.

In similar fashion, it may be shown that the resonant frequency of a given enclosure is 0.35 X the resonant frequency using air, if containing Freon-114 instead. This is a reduction of 1.45 octaves. Expressed otherwise, an enclosure may be constructed having about onethird the volume for a given resonant frequency, if using Freon- 114 instead of air.

It is of particular interest that the resonant frequency of a resonator is dependent largely on the sound velocity and density of the gas in and near its aperture or duct, being little affected by the characteristics of the gas occupying the interior of the resonator, where compressibility, nearly the same in all gases, is the dominant factor.

Loudspeaker apertures exhibit a sharp attenuation, or low frequency cutoff as wavelengths become greater than the circumference of the aperture. For any given frequency, the wavelength in Freon-114 is 0.35 that in air, thus there is a reduction of 1.45 octaves for this low frequency cutoff of an aperture of given size, when using Freon-114 as the acoustic medium, rather than air.

It can also be shown that the accession to inertia of a surface vibrating in Freon-114 is 6.15 X as great as in the case of air. This considerable increase in accession to inertia has a marked effect in improving the fidelity with which the sound wave in the acoustic medium follows the electrical signal driving the vibrating surface.

The reduction of sound velocity to 0.35 X that of air by using Freon-114 as the coupling medium improves the TABLE I.CHARAOTERISTICS OF CERTAIN GASES [1 atmosphere and F.]

acoustically apparent stiffness of the cone of a speaker, as a given impulse moves along the cone surface much faster in relation to the travel of the same impulse of sound moving outward from the apex in the Freon114. At the same time, the increased acoustical impedance tends to hold to lower orders and to lower amplitudes, Whatever vibrational modes do exist in the cone itself.

The examination of mathematical expressions involved with the overall size and shape of horns will show similar marked increases in coupling effectiveness when using Freon-114 as the coupling medium, and such horns will flare more rapidly, be shorter, smaller in aperture and volume, and will yield improved sound quality for a given frequency range requirement, in comparison with horns designed to use air as the acoustic coupling medium. Likewise, with their diaphragms coupled by Freon-114 rather than air, the drive units and reproducers associated with horns are more eflicient and may be reduced in size, and also will require less powerful amplifiers for a given acoustical output.

While it would. be impractical to provide a dense gas coupling medium carried to any extensive distance beyond the aperture of the enclosure or horn of a loudspeaker system in order to benefit fully from the increased accession to inertia outside of the acoustic coupling device involved, its use within that aperture and carried to some lesser distance in front of the aperture and suitably confined by a membrane will afford improved radiation, the dense gas just in front of the taperture affording better coupling with the gas in and near the aperture. A membrane comprising the free air aperture may be made somewhat larger than the aperture of the horn or of the chamber for the dense gas portion confined in front of the cone of a speaker in an enclosure. At the membrane, there is excellent coupling with the free air atmosphere. Also, there is a refraction here of the higher frequencies that tends to increase any angularity with the axis f the loudspeaker system, analogous to the prismatic dispersion of light in emerging from glass after striking the surface at an angle.

The effects on frequency response resulting from the use of Freonl 14 rather than air as the acoustic coupling medium in a fully closed enclosure mounting a speaker cone behind a controlled tension membrane as provided by this invention, can be seen in examining the conventional A.C. circuit analogy for such an arrangement, a series L-C-R circuit. Such a circuit represents the mass, compliance and resistance of the acoustic elements involved. The 6 higher mass of the dense gas and its one-third sound velocity asrcompared with air, lower the resonant frequency and raise the motional impedance considerably. The 1.3x greater compliance in the gas itself further lowers resonant frequency, reducing as well, acceleration time for the cone in reaching any given velocity. The 2.16 higher mechanical resistance lowers the Q of the circuit, flattening frequency response to a degree, as well as materially increasing the coupling efficiency and hence the acoustic output. The effects lowering the resonant frequency are offset by the effect of the added compliance of the membrane. If this added compliance is kept very large, it will have little influence on resonant frequency. Equalizing the pressure on both sides of a membrane with an accommodator can keep this compliance relatively high and within a reasonably narrow range of values. A high tensile strength membrane such as Mylar introduces less compliance than a membrane of lesser tensile strength.

Plastic film, such as Mylar and Saran, quarter mil gauge, having, in some cases, an aluminized surface and acrylic lacquer coatings, have been found satisfactory as impermeable membranes.

Freon-114 and Freon-l2 are both useful as dense gas coupling mediums. Freon-114 has very high density and very low sound velocity, but liquefies at atmospheric pressure at about 38 R, if pure. The admixture of other gases with it can reduce this liquefaction temperature to any desired point. Freon-12 remains a gas to 21.6 F. at atmospheric pressure.

An accommodator to compensate for expansion and contraction of the enclosed gas is essential for maintaining a uniform, high quality of reproduction. Any of several accommodator means are used, one of the simplest and cheapest being an impermeable, flaccid bellows communicating with the confined gas portions. One arrangement is a bellows fitted, at its maximum expansion, to the interior of an enclosure, with the speaker and its panel acting as a fixed wall for the bellows, the bellows and the acoustic charnber thus sharing the same volume of space.

Accommodation may also be accomplished with a small reversible compressor which pumps gas to and from a container of the dense gas (in liquid phase at atmospheric temperature due to being under pressure), or by various thermal liquefaction means, which cool or warm an insulated container of the dense gas (in liquid phase at atmospheric pressure due to being at low temperature), in any case, withdrawing or providing gas as required. Compression systems can automatically purge the enclosed dense gas of accumulated components of air that may slowly diffuse inwardly through the membrane.

Replenishment gas may be supplied to the closed system by use of a diffusion type pressure reducer, passing resupply quantities of dense gas from a container under pressure at some very slow, predetermined rate. This gas may be utilized in any of several ways for sweeping out accumulations of inwardly diffused components of air, although such diffusion results in significant dilution only after a period of several years.

Determining the degree of purity within the system is desirable to assure operation at full effectiveness in frequency range, efficiency and tonal quality.

The following range of values for density and percentage of Freon-114 as related to sound velocity is illustrative: 1

TABLE II.DENS1TY AND CONTENT OF FREON-IM VS. SOUND VELOCITY Sound Velocity, Density, 1b./cu. Content of ft. see. it. Freon-114,

percent Sound velocity may be measured by actuating internal resonators within the dense gas coupling medium and measuring the frequency, or by timing the travel of acoustic signals across a given distance within the medium, using a variety of measuring methods. Testing samples extracted from the system in separate measuring devices eliminates the cost of including testing components in loudspeaker systems.

I claim:

1. In combination,

a sound generator diaphragm,

acoustically conducting means confining a dense gas portion in front of the diaphragm,

means confining a dense gas portion at the rear of the diaphragm,

a small communicating means or capillary joining the front and rear portions of gas,

and an accommodator or compensation apparatus communicating with the portions of gas and reacting to ambient effects, accommodating, as required, ambient effects on said portions of gas, by withdrawing or providing gas, as required.

2. In combination,

a sound generator diaphragm,

acoustically conducting means confining a dense gas portion in front of the diaphragm,

means confining a dense tgas portion at the rear of the diaphragm, a small communicating means or capillary joining the front and. rear portions of gas, and an accommodator or compensation apparatus communicating with the portions of gas and reacting to ambient eflects, accommodating, as required, ambient effects on said portions of .gas, by withdrawing or providing gas, as required, in which an acoustic coupling device comprises a portion of said acoustically conducting means. 3. The combination of claim 1, in which said accommodator comprises a bellows means. 4. The combination of claim 1, in which said acoommod'ator comprises a bellows means having a piston element actuated by a substantially constant-force device, as a weight or spring, affording pressure bias in the confined gas portions. 5. The combination of claim 1, in which said accommodator comprises: a compressor means, a suitably powered electric motor drivingly connected thereto, a container for dense gas in liquid phase, communicating with said compressor means, and volume-sensitive control means communicating with the confined portions of dense gas and interposed between said motor and its source of power. 6. The combination of claim 1, in which said accommodator comprises:

a suitably powered thermoelectric cooling element, an insulated container for dense gas in liquid phase, thermally coupled to said cooling element, and volume-sensitive control means communicating with the confined portions of dense gas and interposed between said cooling element andits source of power. 7. The combination of claim 1, in which said accommodator comprises:

a suitably powered cooling element,

a container for dense gas in liquid phase,

an insulating container comprising chambers,

a variable thermal coupling means regulating thermal coupling of said container for dense gas in liquid phase with said cooling element and with the atmosphere,

and volume-sensitive control means communicating with the confined portions of dense gas, regulating said variable thermal coupling means.

8. The combination of claim 1, in which a suitably powered electric heating element thermally coupled to a portion of the confined dense gas, and a volume-sensitive control means communicating with the confined portions of dense gas and interposed between said heating element and its source of power together comprise a portion of said accommodator.

9. The combination of claim '1, in which a membrane mounted in a movable member comprises a portion of said acoustically conducting means.

10. The combination of claim 1, in which a membrane mounted in an elastomer comprises a portion of said acoustically conducting means.

References Cited by the Examiner UNITED STATES PATENTS 1,730,528 10/1929 Robbins l81--31 1,730,530 lO/1929 Robbins 181-31 1,730,532 10/1929 Robbins 18131 2,115,129 4/1938. Thienhaus 181-31 2,390,847 12/1945 Olson 181-05 2,616,984 11/1952 Pare 179-101 2,797,766 7/1957 Sullivan 18131 2,856,022 10/1958 Kurtze et al. 1810.5 3,170,483 2/1965 Milroy 137553 RICHARD B. WILKINSON, Primary Examiner.

STEPHEN J. TOMSKY, ROBERT H. ROSE,

Examiners.

F. N. CARTEN, Assistant Examiner. 

1. IN COMBINATION, A SOUND GENERATOR DIAPHRAGM, ACOUSTICALLY CONDUCTING MEANS CONFINING A DENSE GAS PORTION IN FRONT OF THE DIAPHRAGM, MEANS CONFINING A DENSE GAS PORTION AT THE REAR OF THE DIAPHRAGM, A SMALL COMMUNICATING MEANS OR CAPILLARY JOINING THE FRONT AND REAR PORTIONS OF GAS, AND AN ACCOMMODATOR OR COMPENSATION APPARATUS COMMUNICATING WITH THE PORTIONS OF GAS AND REACTING TO AMBIENT EFFECTS, ACCOMMODATING, AS REQUIRED, AMBIENT EFFECTS ON SAID PORTIONS OF GAS, BY WITHDRAWING OR PROVIDING GAS, AS REQUIRED. 